Enhanced multimedia call control in next generation mobile communication systems

ABSTRACT

A network-based solution of supporting IP multimedia subsystem (IMS) call setup in a next generation system (5GS) is proposed. During an attach or registration area update procedure, a serving base station sends an indication to a UE indicating whether IMS voice over PS session is supported or not. Upon receipt of the indication that IMS VoPS is supported, the UE triggers an IMS registration procedure. However, when an MO/MT call happens, the network determines that the UE may be in conditions where voice service is not supported because the network is not able to provide a successful IMS VoPS over the current serving cell connected to 5G core network. The network then triggers a RAT change or a EPS fallback procedure such that the UE is handover to a target cell that supports IMS VoPS.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 from U.S.Provisional Application No. 62/419,953, entitled “Enhanced MultimediaCall Control”, filed on Nov. 9, 2016, the subject matter of which isincorporated herein by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communication,and, more particularly, to method of supporting multimedia services innext generation mobile communication systems.

BACKGROUND

The wireless communications network has grown exponentially over theyears. A Long-Term Evolution (LTE) system offers high peak data rates,low latency, improved system capacity, and low operating cost resultingfrom simplified network architecture. LTE systems, also known as the 4Gsystem, also provide seamless integration to older wireless network,such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS).In LTE systems, an evolved universal terrestrial radio access network(E-UTRAN) includes a plurality of evolved Node-Bs (eNodeBs or eNBs)communicating with a plurality of mobile stations, referred to as userequipments (UEs). The 3^(rd) generation partner project (3GPP) networknormally includes a hybrid of 2G/3G/4G systems. With the optimization ofthe network design, many improvements have developed over the evolutionof various standards.

As set forth in the 3GPP, IP Multimedia Subsystem (IMS) is a corenetwork that provides IP multimedia services to user equipments (UEs)over an Internet Protocol (IP) network. Historically, mobile phones haveprovided voice call services over a circuit-switched (CS) network,rather than strictly over an IP packet-switched (PS) network.Alternative methods of delivering voice or other multimedia servicesover IP have become available on smartphones (e.g. VoIP or Skype), butthey have not become standardized across the industry. IMS is anarchitectural framework to provide such standardization. IMS is able tocommunicate with UEs through different types of access network, such asa wireless local area network (WLAN), an Ethernet network, a packet datanetwork (PDN), or another type of access network. IMS is a new way todial PS call on LTE (Voice over IP or Voice over LTE) instead offallback to 2G/3G legacy CS call.

The Next Generation. Mobile Network (NGMN) board, has decided to focusthe future NGMN activities on defining the end-to-end requirements for5G. Voice service will be an important feature for the next generationsystem, e.g., NG system (NGS) or 5G system (5GS). It is proposed thatthe NG/5G systems shall support IMS PS voice service, IMS PS voiceservice continuity with the 4G evolved packet system (EPS) and INS PSvoice service fallback to EPS. However, when a voice call triggered, aUE may be in conditions where voice service is not supported. In thiscase, the UE shall move to a proper access or core system to continuethe voice call setup.

Solutions for IMS call setup in NGS/5GS when the serving cell in NGS/5GSis unable to support multimedia calls are sought.

SUMMARY

A network-based solution of supporting IP multimedia subsystem (IMS)call setup in a next generation system (5GS) is proposed. During anattach or registration area update procedure, a serving base stationsends an indication to a UE indicating whether IMS voice over PS sessionis supported or not. Upon receipt of the indication that IMS VoPS issupported, the UE triggers an IMS registration procedure. However, whena mobile originated or mobile terminated (MO/MT) call happens, thenetwork determines that the UE may be in conditions where voice serviceis not supported because the network is not able to provide a successfulIMS VoPS over the current serving cell connected to 5G core network. Thenetwork then triggers a RAT change or a EPS fallback procedure such thatthe UE is handover to a target cell that supports IMS VoPS.

In one embodiment, a base station transmits information related to IPMultimedia Subsystem (IMS) to a user equipment (UE) in a Next Generation(NG) serving cell connected to a 5G core network. The informationindicates IMS voice over PS session is supported over a 5G system (5GS).The base station receives an IMS call indication from an IMS server viathe 5GC. The base station determines whether IMS voice over PS sessionis supported over the NG serving cell with a predefined QoS requirement.The base station sends a handover command to the UE if the current NGserving cell does not support IMS VoPS. The UE is handover from thecurrent NG serving cell to a target cell that supports IMS VoPS.

In another embodiment, a UE receives an indication indicates that IPmultimedia subsystem (IMS) voice over PS session is supported in a 5GS.The UE performs IMS registration with an IMS server, and subsequentlythe UE is originating or terminating an IMS voice call. The UE receivesa handover command when IMS voice over PS session is not supported overthe NG service cell with a predefined Quality of Service (QoS)requirement, and the UE handover from the NG serving cell to a targetcell that supports IMS VoPS. The UE performs IMS voice call setupthrough the IMS server in the target cell.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 illustrates an exemplary next generation system with multipleaccess and core networks and a user equipment (UE) supporting IPmultimedia subsystem (IMS) call setup in accordance with one novelaspect.

FIG. 2 illustrates simplified block diagrams of a user equipment (UE)and a base station (BS) in accordance with embodiments of the currentinvention.

FIG. 3 illustrates interworking and migration for IMS call setup supportin 5GS in accordance with embodiments of the current invention.

FIG. 4 illustrates an example of IMS registration process in 5GS inaccordance with embodiments of the current invention.

FIG. 5 illustrates a first embodiment of a network-based solution forsupporting IMS call setup in a next generation system in accordance withembodiments of the current invention.

FIG. 6 illustrates a second embodiment of a network-based solution forsupporting IMS call setup in a next generation system in accordance withembodiments of the current invention.

FIG. 7 illustrates a sequence flow of supporting an IMS voice call setupin accordance with a novel aspect of the current invention.

FIG. 8 is a flow chart of a method of performing IMS call setup from abase station perspective in accordance with a novel aspect.

FIG. 9 is a flow chart of a method of performing IMS call setup from auser equipment perspective in accordance with a novel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 illustrates an exemplary next generation system 100 with multipleradio access and core networks and a user equipment (UE) supporting IPmultimedia subsystem (IMS) call setup in accordance with one novelaspect. Next generation mobile communication system 100 comprises radioaccess networks 111, core networks 112, and application serversincluding an IP multimedia subsystem (IMS) server 106. Radio accessnetworks RAN 111 provide radio access for UE 101 via various radioaccess technologies (RATs). For example, RAN 111 may include an E-UTRAN107 having a base station 102 and an NG RAN (NR) 108 having a basestation 103. Core networks CN 112 provide services for UE 101 via anLTE/4G evolved packet core (EPC) 104 or via a next generation 5G corenetwork (5GC) 105. UE 101 may be equipped with a single radio frequency(RF) module or transceiver or multiple RF modules or transceivers forservices via different RATs/CNs. UE 101 may be a smart phone, a wearabledevice, an Internet of Things (IoT) device, a tablet, etc.

IP Multimedia Subsystem (IMS) is a core network that provides IPmultimedia services to user equipments (UEs) over an Internet Protocol(IP) network. The Next Generation Mobile Network (NGMN) board, hasdecided to focus the future NGMN activities on defining the end-to-endrequirements for 5G. Voice service will be an important feature for thenext generation system, e.g., NG system (NGS) or 5G system (5GS). It isproposed that the NG/5G systems shall support IMS PS voice service, IMSPS voice service continuity with the 4G evolved packet system (EPS), andIMS PS voice service fallback to EPS. However, when a voice call istriggered, a UE may be in conditions where voice service is notsupported. In this case, the UE shall move to a proper access or corenetwork to continue the voice call setup.

In accordance with one novel aspect, a network-based solution forsupporting IMS call setup in a next generation NG/5G system is proposed.In the example of FIG. 1, UE 101 is initially served by base station 103in an NG RAN 108 connected to 5GC 105. During an attach or registrationarea update procedure, the serving base station 103 will send anindication toward UE 101—informing UE 101 whether IMS voice over PSsession is supported or not supported. A UE with “IMS voice over PS”voice capability will take this indication into account when performingvoice domain selection. Upon receipt of the indication that IMS VoPS issupported, UE 101 triggers the IMS registration procedure if it is IMSunregistered. In FIG. 1, UE 101 is already IMS registered andestablishes an IP connection #1 via NG RAN 108 and 5GC 105 to beconnected to application servers. UE 101, however, may be in conditionswhere voice service is not supported even though UE 101 is already IMSregistered, because the network is not able to provide a successful IMSservice over PS session over NG RAN 108 connected to 5GC 105. In a firstembodiment, E-UTRAN 107 connected to 5GC 105 supports voice, and NG RAN108 is able to trigger handover UE 101 to E-UTRAN 107 connected to 5GC105 and establish IP connection #2 for voice service. In a secondembodiment, UE 101 supports handover to EPS and EPS supports voice, andNG RAN 108 is able to trigger handover UE 101 to E-UTRAN 107 connectedto EPC 104 and establish IP connection #3 for voice service.

FIG. 2 illustrates simplified block diagrams of a user equipment UE 201and a base station BS 202 in accordance with embodiments of the currentinvention. BS 202 may have an antenna 226, which may transmit andreceive radio signals. RF transceiver module 223, coupled with theantenna, may receive RF signals from antenna 226, convert them tobaseband signals and send them to processor 222. RF transceiver 223 mayalso convert received baseband signals from processor 222, convert themto RF signals, and send out to antenna 226. Processor 222 may processthe received baseband signals and invoke different functional modules toperform features in BS/AP 202. Memory 221 may store program instructionsand data 224 to control the operations of BS 202. BS 202 may alsoinclude a set of functional modules and control circuits, such as acontrol and configuration circuit 211 for control and configure IMSrelated features including providing two indicators—“IMS VoPS Supported”and “RAT VoPS Supported”- to UE, a QoS and connection circuit 212 forestablish radio connection with UE that satisfies predefined Quality ofService (QoS) flow requirement, and a handover circuit 213 for sendinghandover commands to UE.

Similarly, UE 201 has an antenna 235, which may transmit and receiveradio signals. RF transceiver module 234, coupled with the antenna, mayreceive RF signals from antenna 235, convert them to baseband signalsand send them to processor 232. RF transceiver 234 may also convertreceived baseband signals from processor 232, convert them to RFsignals, and send out to antenna 235. Processor 232 may process thereceived baseband signals and invoke different functional modules toperform features in the UE 201. Memory 231 may store programinstructions and data 236 to control the operations of the UE 201. UE201 may also include a set of function modules and control circuits thatmay carry out functional tasks of the present invention. An attach andconnection circuit 291 may attach to the network and establishconnection with serving base station, an IMS registration circuit 292may perform IMS registration with IMS server, a voice call and codeccontrol circuit 293 may originate or terminate voice calls and negotiatecodec parameters, and a measurement and handover circuit 294 may performmeasurements and handle handover functions in the network.

The various function modules and control circuits may be implemented andconfigured by software, firmware, hardware, and combination thereof. Thefunction modules and circuits, when executed by the processors viaprogram instructions contained in the memory, interwork with each otherto allow the base station and UE to perform embodiments and functionaltasks and features in the network. In one example, each module orcircuit comprises a processor (e.g., 222 or 232) together withcorresponding program instructions.

FIG. 3 illustrates interworking and migration for IMS call setup supportin 5GS in accordance with embodiments of the current invention.Deployment based on different 3GPP architectures (i.e. EPC based or 5GCbased) and UEs with different capabilities (EPC NAS and 5GC NAS) maycoexist at the same time within one PLMN. UE will use EPC NAS or 5GC NASprocedures depending on the core network by which it is served. In orderto interwork with EPC, UE that supports both 5GC and EPC NAS can operatein single-registration mode or dual-registration mode. PDN sessions canbe transferred from 5GC to EPC or from EPC to 5GC for UEs insingle-registration or dual-registration mode for mobility. In oneexample, UEs with dual-registration mode may be used for IMS voice.

In the example of FIG. 3, In order to support smooth migration, it isassumed that the EPC 311 and the 5GC 312 have access to a commonsubscriber database 301, that is HSS in case of EPC and UDM in case of5GC, acting as the master database for a given UE. E-UTRAN 321 connectsto EPC 311 via S1 interface; E-UTRAN 322 connects to EPC 311 via S1interface, and connects to 5GC 312 via N2/N3 interface; NG RAN 323connects to 5GC 312 via N2/N3 interface. E-UTRAN 322 and NG RAN 323 areinter-connected. From UE perspective, EPC UE 331 supports E-UTRA only;EPC UE 332 supports E-UTRA+5G RAN dual connectivity; N1 UE 333 supportsE-UTRAN with or without 5G RAN dual connectivity; N1 UE 334 supports NGRAN with or without dual connectivity with E-UTRAN.

Note that in this network architecture, 5GC 312 can connect both NG RAN323 and E-UTRAN 322, and E-UTRAN 322 can connect both EPC 311 and 5GC312. In one example, when a UE that supports camping on 5G system with5GC NAS, it can perform initial access either through E-UTRAN thatconnects to 5GC or through NG RAN towards 5GC. The UE can also performinitial access through E-UTRAN towards EPC if supported and needed.Further, the UE can perform EPC NAS or 5GC NAS procedures over E-UTRANor NG RAN respectively for mobility management and session managementdepending on capability indicated in AS layer if the UE also supportsEPC NAS. Under this network architecture, the UE can preferably stay in5GS and can select IMS domain for originating call, regardless ofwhether voice actually supported over the RAT the UE is camped on. Thisis because that the UE can be indicated with “IMS voice over PSsupported” via IMS registration procedure. This indication indicatesthat the network is able to provide a successful IMS voice over PSsession over NG RAN connected to 5GC, or the NG RAN can trigger tohandover the UE to E-UTRAN connected to 5GC or handover to EPS when thenetwork is not able to provide a successful IMS over PS session over NGRAN connected to 5GC.

FIG. 4 illustrates an example of IMS registration process in 5GS inaccordance with embodiments of the current invention. Two indicationsare introduced to facilitate the multimedia call setup. A firstindication is “IMS VoPS Supported” indication, it indicates whether IMSvoice over PS session is supported over the NG core, e.g., 5GC. Ifsupported, the UE registers to IMS to ensure reachability for multimediacalls. A second indication is “RAT VoPS Supported” indication, itindicates whether IMS voice over PS session is supported in the servingNG RAT or NG serving cell. This indication is considered valid by the UEif “IMS VoPS Supported” is TRUE. “RAT VoPS Supported” indication isbroadcasted by NG RAN as part of the System Information of the cell.Alternatively, this indication can be maintained at registration arealevel, and be transmitted by signaling from the 5GC via Attach orRegistration Area Update procedure.

The UE IMS registration status follows the “IMS VoPS Supported”indication. In the example of FIG. 4, in step 411, UE 401 is in CN idlemode, and is IMS un-registered initially. In step 412, UE 401 attachesto the network or performs non-periodic registration area update, andreceives a message with “IMS VoPS Supported=TRUE” indication from 5GC403. Upon receipt of the indication that IMS VoPS is supported, the UEtriggers the IMS registration procedure if it is IMS unregistered. Instep 413, UE 401 performs IMS registration with IMS server 404accordingly. In step 414, UE 401 is in CN connected mode and is IMSregistered. The 5GC 403 indicates IMS voice over PS session supported inone of the following cases: 1) the network is able to provide asuccessful IMS voice over PS session over NG RAN 402 connected to 5GC403 with a 5G QoS flow that supports voice service with a predefined QoSrequirement. 2) the network is not able to provide a successful IMSvoice over PS session over NG RAN 402 connected to 5GC 403, but is ablefor one of the following: 2a) if an E-UTRAN connected to 5GC supportsvoice, and the NG RAN 402 is able to trigger handover to the E-UTRANconnected to 5GC 403 at QoS flow establishment for voice with QoS; or2b) if the UE supports handover to an EPS, the EPS supports voice, andthe NG RAN 402 is able to trigger handover to EPS at QoS flowestablishment for voice with QoS. Therefore, in summary, the “IMS VoPSSupported” indication indicates whether IMS voice over PS session issupported over 5GS, which includes (5GC+NG RAN) and/or (5GC+E-UTRAN).

FIG. 5 illustrates a first embodiment of a network-based solution forsupporting IMS call setup in a next generation system in accordance withembodiments of the current invention. The next generation systemcomprises a UE 501, 5GS 502 including NG RAN 503 and 5GC 504, EPS 505including E-UTRAN 506 and EPC 507, and IMS server 508. In thisembodiment, UE 501 is initially in CN connected mode, and is already IMSregistered. UE 501 has received an IMS VoPS Support indication from 5GC504 indicating voice over PS Session is supported in 5GC 504. For MobileOriginated (MO) call, UE 501 triggers the MO call in step 511 and sendsout SIP invite to IMS server 508 in step 512. For Mobile Terminated (MT)call, IMS server 508 triggers the MT call in step 513. In step 521,optionally, SIP/SDP codec negotiation occurs between UE 501 and IMSserver 508. In step 531, IMS server 508 sends a call indication to 5GC504 for checking if UE 501 is currently in a voice-capable RAT/cell. Thecall indication includes information such as IP, port, and media type.In step 541, the 5GS determines that the UE's current RAT or servingcell is not voice-capable. The determination in step 541 can be made bythe core network 5GC 504 or the access network NG RAN 503. The 5GC/NGRAN is aware of the value of the RAT VoPS Supported indicationassociated with UE and RAN based on UE/RAN radio capability. In oneexample, RAN can directly decide whether IMS VoPS is supported (i.e.,improper frequency band). In another example, RAN can decide whether IMSVoPS is supported for the UE. When the indication “RAT VoPSSupported=FALSE” triggers a RAT change procedure.

In order to trigger the RAT change procedure, the 5GS further determinesthat there is another RAN, e.g. E-UTRAN 506 that is also connected to5GC 504 for QoS flow establishment for voice, so that E-UTRAN 506 can beselected as the target cell for handover. In one example, the targetcell is an LTE cell that supports voice calls. In another example, thetarget cell is an NG cell operating in a proper frequency band (e.g., alow frequency band) that also supports establishing a quality of service(QoS) flow for IMS voice calls. In step 551, 5GC 504 sends out ahandover command, which is forwarded to UE 501 by NG RAN 503. In step561, UE 501 moves to the target cell, e.g., E-UTRAN 506 that isconnected to 5GC 504. In step 571, UE 501 performs voice call setupprocedure through IMS server 508. Note that the SIP/SDP CodecNegotiation occurred in step 521 can be merged into the voice call setupprocedure of step 571.

FIG. 6 illustrates a second embodiment of a network-based solution forsupporting IMS call setup in a next generation system in accordance withembodiments of the current invention. The next generation systemcomprises a UE 601, 5GS 602 including NG RAN 603 and 5GC 604, EPS 605including E-UTRAN 606 and EPC 607, and IMS server 608. In thisembodiment, UE 601 is initially in CN connected mode, and is already IMSregistered. UE 601 has received an IMS VoPS Support indication from 5GC604 indicating Voice over PS Session is supported in 5GC 604. For MobileOriginated (MO) call, UE 601 triggers the MO call in step 611 and sendsout SIP invite to IMS server 608 in step 612. For Mobile Terminated (MT)call, IMS server 608 triggers the MT call in step 613. In step 621,optionally, SIP/SDP codec negotiation occurs between UE 601 and IMSserver 608. In step 631, IMS server 608 sends a call indication to 5GC604 for checking if UE 601 is currently in a voice-capable RAT/cell. Thecall indication includes information such as IP, port, and media type.In step 641, the 5GS determines that the UE's current RAT or servingcell is not voice-capable. The determination in step 641 can be made bythe core network 5GC 604 or the access network NG RAN 603. The 5GC/NGRAN is aware of the value of the RAT VoPS Supported indication. That is,the indication “RAT VoPS Supported=FALSE” triggers an EPS fallbackprocedure.

In order to trigger the EPS fallback procedure, the 5GS furtherdetermines that EPS fallback is required because there is no othervoice-capable RAN can be selected as a target cell that is alsoconnected to 5GC 604. As a result, UE 601 needs to be handover to EPSthat supports voice. In step 651, 5GC 604 sends out a handover command,which is forwarded to UE 501 by NG RAN 603. In step 661, UE 601 moves tothe target cell, e.g., E-UTRAN 606 that is connected to EPC 607. In step671, UE 601 performs tracking area update (TAU) procedure or Attachprocedure with EPC 607. Those procedures are required for interworkingbetween 5GS and EPS. UE selects one of those two procedures based onwhether the UE operates in Single Registration Mode (SRM) or DualRegistration Mode (DRM), and whether the core networks support N26interface between EPS and 5GS. In step 681, UE 601 performs IMS voicecall setup procedure through IMS server 608 in E-UTRAN 606 over EPC 607.Note that the SIP/SDP Codec Negotiation occurred in step 621 can bemerged into the voice call setup procedure of step 681.

FIG. 7 illustrates a sequence flow of supporting an IMS voice call setupin accordance with a novel aspect of the current invention. In step 711,UE 701 performs an attach or a registration area update procedure to 5GS702, which comprises an NG RAN and a 5G core network. 5GS 702 sends an“IMS VoPS Supported=TRUE” indication to UE 701. In step 712, UE 701triggers an IMS registration procedure with IMS server 704 and becomesIMS registered. In step 721, UE 701 initiates an MO call and sends anSIP invite to IMS server 704. Alternatively, IMS server 704 initiates anMT call in step 723. In step 724, IMS server 704 sends an IMS callindication to 5GS 702. Upon receive the call indication, in step 731,5GS determines whether the current serving cell supports VoPS by anindication, RAT VoPS Supported. If the indication RAT VoPSSupported=FALSE for the NG RAN for UE 701, then in step 732, 5GS 702determines whether to trigger a RAT change or an EPS fallback procedure.In step 741, 5GS 702 sends a handover command to UE 701. In step 751, UE701 handover from the current NG serving cell to a target cell thatsupports IMS VoPS. The target cell is connected to the 5GC for RATchange. Alternatively, the target cell is connected to an EPC for EPSfallback. In step 761, UE 701 performs IMS call setup through the IMSserver 704 and completes the call setup procedure.

FIG. 8 is a flow chart of a method of performing IMS call setup from abase station perspective in accordance with a novel aspect. In step 801,a base station transmits information related to IP Multimedia Subsystem(IMS) to a user equipment (UE) in a Next Generation (NG) serving cellconnected to a 5G core network. The information indicates IMS voice overPS session is supported over the 5G core network. In step 802, the basestation receives an IMS call indication from an IMS server via the 5GC.In step 803, the base station determines whether IMS voice over PSsession is supported over the NG serving cell with a predefined QoSrequirement. In step 804, the base station sends a handover command tothe UE if the current NG serving cell does not support IMS VoPS. The UEis handover from the current NG serving cell to a target cell thatsupports IMS VoPS. In one embodiment, the handover command is triggeredby a RAT change, wherein the target cell is connected to the 5G corenetwork. In another embodiment, the handover command is triggered by anevolved packet system (EPS) fallback procedure, and the target cell isnot connected to the 5G core network.

FIG. 9 is a flow chart of a method of performing IMS call setup from auser equipment perspective in accordance with a novel aspect. In step901, the UE receives an IP multimedia subsystem (IMS) voice over PSsession is supported indication in a next generation (NG) serving cellconnected to a 5G core network. In step 902, the UE performs IMSregistration with an IMS server, and subsequently the UE is originatingor terminating an IMS voice call. In step 903, the UE receives ahandover command when IMS voice over PS session is not supported overthe NG service cell with a predefined Quality of Service (QoS)requirement, and the UE handover from the NG serving cell to a targetcell that supports IMS VoPS. In step 904, the UE performs IMS voice callsetup through the IMS server in the target cell.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method, comprising: transmitting informationrelated to IP Multimedia Subsystem (IMS) from a serving base station toa user equipment (UE) in a Next Generation (NG) serving cell connectedto a 5G core network, wherein the information indicates IMS voice overPacket Switched (PS) session is supported over the 5G core network;receiving an IMS call indication from an IMS server via the 5G corenetwork; determining whether IMS voice over PS (VoPS) session issupported over the NG serving cell with a predefined Quality of Service(QoS) requirement; and generating a handover command to the UE upondetermining that the current NG serving cell does not support IMS VoPS,wherein the base station triggers a handover for the UE from the currentNG serving cell to a target cell that supports IMS VoPS for performingan IMS VoPS call setup.
 2. The method of claim 1, wherein the targetcell is another NG cell that supports IMS VoPS.
 3. The method of claim1, wherein the target cell is a 4G LTE cell that supports IMS VoPS. 4.The method of claim 1, wherein a first indication indicates whether IMSvoice over PS session is supported over a 5G system.
 5. The method ofclaim 1, wherein a second indication indicates whether IMS voice over PSsession is supported over the NG serving cell.
 6. The method of claim 1,wherein the handover command is triggered by a Radio Access Technology(RAT) change, and wherein the target cell is connected to the 5G corenetwork.
 7. The method of claim 1, wherein the handover command istriggered by an evolved packet system (EPS) fallback procedure, andwherein the target cell is not connected to the 5G core network.
 8. Abase station, comprising: a radio frequency (RF) transmitter thattransmits information related to IP Multimedia Subsystem (IMS) from abase station to a user equipment (UE) in a Next Generation (NG) servingcell connected to a 5G core network, wherein the information indicatesIMS voice over Packet Switched (PS) session is supported over the 5Gcore network; an RF receiver that receives an IMS call indication froman IMS server via the 5G core network; a Quality of Service (QoS)circuit that determines whether IMS voice over PS (VoPS) session issupported over the NG serving cell with a predefined QoS requirement;and a handover circuit that generates a handover command to the UE upondetermining that the current NG serving cell does not support IMS VoPS,wherein the base station triggers a handover for the UE from the currentNG serving cell to a target cell that supports IMS VoPS for performingan IMS VoPS call setup.
 9. The base station of claim 8, wherein thetarget cell is another NG cell that supports IMS VoPS.
 10. The basestation of claim 8, wherein the target cell is a 4G LTE cell thatsupports IMS VoPS.
 11. The base station of claim 8, wherein a firstindication indicates whether IMS voice over PS session is supported overa 5G system.
 12. The base station of claim 8, wherein a secondindication indicates whether IMS voice over PS session is supported overthe NG serving cell.
 13. The base station of claim 8, wherein thehandover command is triggered by a Radio Access Technology (RAT) change,and wherein the target cell is connected to the 5G core network.
 14. Thebase station of claim 8, wherein the handover command is triggered by anevolved packet system (EPS) fallback procedure, and wherein the targetcell is not connected to the 5G core network.
 15. A method, comprising:receiving an IP multimedia subsystem (IMS) voice over Packet Switched(PS) session is supported indication by a user equipment (UE) in a nextgeneration (NG) serving cell connected to a 5G core network; performingIMS registration with an IMS server, wherein subsequently the UE isoriginating or terminating an IMS voice call; receiving a handovercommand when IMS voice over PS (VoPS) session is not supported over theNG service cell with a predefined Quality of Service (QoS) requirement,wherein the UE handover from the NG serving cell to a target cell thatsupports IMS VoPS; and generating an IMS voice call setup through theIMS server in the target cell.
 16. The method of claim 15, wherein thehandover command is triggered by a Radio Access Technology (RAT) change,and wherein the target cell is connected to the 5G core network.
 17. Themethod of claim 16, wherein the target cell is either another NG cell ora 4G LTE cell that supports IMS VoPS.
 18. The method of claim 15,wherein the handover command is triggered by an evolved packet system(EPS) fallback procedure, and wherein the target cell is not connectedto the 5G core network.
 19. The method of claim 18, wherein the UEperforms a tracking area update (TAU) procedure or an Attach procedurewith an evolved packet core network (EPC) after handover.
 20. The methodof claim 15, wherein the UE performs codec negotiation with the IMSserver before or after the handover.